This invention relates to a navigation apparatus, and more particularly to a navigation apparatus wherein a guide screen for guiding a vehicle, during traveling, to a destination along a guide route, is displayed on a display apparatus.
In a navigation apparatus which guides a vehicle during traveling to allow a driver to arrive readily at a desired destination, the position of the vehicle is detected and map data around the position of the vehicle is read out from a CD-ROM (compact disk read only memory). Then, an image of the map is drawn on a display screen, and a vehicle position mark (self-vehicle position mark) is drawn in an overlapping relationship at a predetermined location on the image of the map. Then, as the current position varies due to movement of the vehicle, the self-vehicle position mark on the screen is moved or alternatively, the self-vehicle mark is fixed at a predetermined position such as the center of the screen, while the map is scrolled so that map information around the vehicle position may always be observed at a glance.
A navigation apparatus of the type described above has a route guiding function for setting a guide route from a starting point to a destination, displaying the guide route on a map and giving intersection guidance which is an enlarged view of the intersection and the advancing direction of the vehicle. If a starting point and a destination are inputted, then a guide route controller of the navigation apparatus automatically determines an optimum guide route, and successively stores in a guide route memory, nodes (longitudes and latitudes) which define the guide route. Then, upon actual traveling, a portion of the guide route which is included in a map display area of the screen is searched from among the train of nodes stored in the guide route memory, and the guide route portion searched out or determined is displayed in a manner which distinguishes it from other roads. Further, when the vehicle reaches a predetermined distance from an approaching intersection to which the vehicle is advancing, an intersection location map (an enlarged view of the intersection and an arrow mark indicating a direction in which the vehicle is to advance across the intersection) is displayed so that the driver can recognize which road the vehicle should advance along or in which direction the vehicle should advance. Further, if the vehicle goes off of the guide route and enters an off-route condition, then the navigation apparatus searches for (calculates) a route from the current position of the vehicle to a suitable return point on the guide route so that it guides the vehicle to the destination via the return point.
FIG. 15 is a schematic view of an example of a guide route display. Referring to FIG. 15, a self-vehicle mark is denoted at CM, a guide route RT is denoted by a broken line, and an intersection enlarged view of an intersection Q is denoted at ELI. In the intersection enlarged view ELI of intersection Q, intersection composing links B1 to B4 are first represented by link figures of a predetermined thickness, and then the link figure representations are converted into and displayed in a perspective view. To each link, the name of a location to which the link leads (Ohmiya, Tokorozawa, Urawa Station and Nihonbashi in FIG. 15) is additionally displayed, and an arrow mark ARR indicating the direction of the guide route is displayed. In order to draw the intersection enlarged view, the circumferential angle of 360.degree. around the intersection Q is equally divided into eight (8) angular regions with reference to an intersection entering direction, the direction of the link L1 along which the vehicle comes into the intersection as shown in FIG. 16. The eight (8) angular regions are the entering opposite direction region A1, oblique left-downward region A2, left-turn region A3, oblique left-upward region A4, straightforward advancing region A5, oblique right-upward region A6, right-turn region A7 and oblique right-downward region A8. Then, it is determined as to which regions the intersection composing links individually belong, and a intersection enlarged view which has branches in directions corresponding to the angular regions to which the intersection composing links belong, is produced and drawn into an image.
FIG. 17 is a table illustrating messages used for guidance at an intersection by voice. Referring to FIG. 17, guidance is provided such that, for example, when the direction of the outgoing link is the right-turn direction, the voice message "turn to the right ahead" is given, but when the direction of the outgoing link is the oblique right-upward direction, the message "turn to the oblique right-upward ahead" is given. It is to be noted that some navigation apparatus do not give an intersection guidance when a vehicle should advance straightforwardly across an intersection.
The foregoing description relates to a navigation apparatus used in Japan. The navigation apparatus used in United States and some other countries does not display, during traveling of a vehicle, a map image including a map and a vehicle position mark but rather displays such a guide screen as shown in any of FIGS. 18A to 18F and gives a guidance of an advancing direction by voice. In the guide screens of FIGS. 18A to 18F, a distance to an intersection is displayed as CDS, a distance to a destination is displayed at DDS, an indication that guidance by voice is in service is displayed at VCD, a current time is displayed at TDL, and a guide image indicating the advancing direction is displayed at NVG. When an intersection or a branch is not present on a guide route within a predetermined distance from a current position of the vehicle, a guide screen which indicates straightforward advancement, as seen in FIG. 18A, is displayed; when an approaching intersection is present within the predetermined distance, an enlarged view of the intersection or a branch and an arrow mark which indicates an advancing direction are displayed, as seen in FIGS. 18B to 18E; and when a U-turn is required, a U-turn figures as shown in FIG. 18F are displayed. Then, when the vehicle reaches a predetermined distance from a branch or an intersection, the navigation apparatus guides the advancing direction by voice.
As described above, the navigation apparatus in the United States and some other countries detects the position of a vehicle, reads map data corresponding to the vehicle position from a map data base such as a CD-ROM, and if an approaching intersection or branch is determined on the guide route, within a predetermined distance from the current position of the vehicle, displays an enlarged figure of the intersection or branch using map data similar to a display of an enlarged representation of an intersection in Japan and also displays an advancing direction of the vehicle with an arrow mark while giving a guidance of a direction in which the vehicle is to advance by voice. On the other hand, when an approaching branch or intersection is not determined within the predetermined distance, then the navigation apparatus displays a guide screen which indicates straightforward advancement of the vehicle. Then, if the vehicle goes off of the guide route (enters an off-route condition), the navigation apparatus searches for a route from the current position of the vehicle to a predetermined point, the return point, on the guide route and guides the vehicle to a destination via the return point. Further, when a guide route is to be set, the navigation apparatus displays a map image so that a guide route can be set by inputting a starting point and a destination.
Consequently, the navigation apparatus in Japan and the navigation apparatus in the United States have almost the same internal constructions but differ only in the control of the display screen.
As a method of determining the current position of a vehicle using a navigation apparatus, two methods are available including a first self-contained navigation measuring method wherein the position of a vehicle is determined using self-contained distance and orientation sensors carried on the vehicle (a dead reckoning method) and a second satellite navigation method which is based on the GPS (Global Positioning System) which makes use of artificial satellites. The determination of a vehicle position by the self-contained navigation method allows measurement of the vehicle position at a comparatively low cost, but has a problem in that the position cannot be measured with a high degree of accuracy due to errors of the sensors and requires correction processing such as map matching. Meanwhile, the satellite navigation method allows detection of an absolute position, but the measurement position data obtained include drift position errors caused by various factors, and the nominal tolerance of the U.S. organization is less than 100 m (95 percent in accuracy). The satellite navigation method has another problem in that position detection is disabled at a location where radio waves are interrupted such as when the vehicle is in a tunnel or behind a building.
Therefore, a recent vehicle-carried navigation apparatus makes use of both the self-contained navigation method and the satellite navigation method such that a position and an orientation are usually estimated using the self-contained navigation method and the estimated vehicle position is corrected by a map matching process to define an actual vehicle position on a road being traveled. Then, if map matching is disabled by some cause and the vehicle position measured using the self-contained navigation method is displaced by a large amount from the actual vehicle position such that the distance between the measured vehicle position and the vehicle position measured making use of the GPS exceeds an allowable error range, then the vehicle position is corrected to the position measured or determined making use of the GPS, after which the vehicle position is drawn additionally to the traveling road by the map matching process to define the actual vehicle position.
In the self-contained navigation method, the vehicle position is detected by integration based on outputs of the distance sensor and the relative orientation sensor. FIG. 19 illustrates a vehicle position detection method by the self-contained navigation method. Referring to FIG. 19, it is assumed that the distance sensor outputs a pulse each time the vehicle travels a certain unit distance L.sub.0, and the reference orientation (.theta.=0) is set to the positive direction of the X-axis while the counterclockwise direction from the reference orientation is taken as a+direction. The vehicle position in the immediately preceding detection cycle, is represented by a point P.sub.0 (X.sub.0, Y.sub.0), the absolute orientation of the vehicle advancing direction at the point P.sub.0 is represented by .theta..sub.0, and the output of the relative orientation sensor when the vehicle travels the unit distance L.sub.0, is represented by .DELTA..theta..sub.1. The variation of the vehicle position is given by: EQU .DELTA.X=L.sub.0 .multidot.cos (.theta..sub.0 +.DELTA..theta..sub.1) EQU .DELTA.Y=L.sub.0 .multidot.sin (.theta..sub.0 +.DELTA..theta..sub.1)
Consequently, the estimated orientation .theta..sub.1 of the vehicle advancing direction and the estimated vehicle position (X.sub.1, Y.sub.1) of the vehicle at the point P.sub.1 in the current detection cycle can be calculated by vector synthesis using the following equations: EQU .theta..sub.1 =.theta..sub.0 +.DELTA..theta..sub.1 ( 1) EQU X.sub.1 =X.sub.0 +.DELTA.X=X.sub.0 +L.sub.0 .multidot.cos (.theta..sub.0 +.DELTA..theta..sub.1) (2) EQU Y.sub.1 =Y.sub.0 +.DELTA.Y=Y.sub.0 +L.sub.) .multidot.sin (.theta..sub.0 +.DELTA..theta..sub.1) (3)
Accordingly, if absolute orientation and position coordinates of a vehicle at a starting point are given, then each time the vehicle thereafter travels a unit distance, the vehicle position can be detected (estimated) on a real time basis by repeating the calculation of the equations (1) to (3).
With the self-contained navigation method, however, as the travel of the vehicle proceeds, errors are accumulated so that the estimated vehicle position may be displaced from a road. Therefore, the estimated vehicle position is compared with road data to correct the estimated vehicle position to an actual vehicle position on the road by a map matching process. Map matching, based on a projection method, is displayed in FIGS. 20 and 21. Referring to FIGS. 20 and 21, it is assumed that the current vehicle position is a point P.sub.i-1 (X.sub.i-1, Y.sub.i-1) and the vehicle orientation is .theta..sub.i-1 (in FIG. 20, it is shown that the point P.sub.i-1 does not coincide with a road Rda). If the relative orientation when the vehicle travels a fixed distance L.sub.0 (for example, 10 m) from the point P.sub.i-1 is .DELTA..theta..sub.i, then the estimated vehicle position P.sub.i ' (X.sub.i ', Y.sub.i ') and the estimated vehicle orientation .theta..sub.i at the point P.sub.i ' are calculated, by the self-contained navigation method, using the following equations: EQU .theta..sub.i =.theta..sub.i-1 +.DELTA..theta..sub.i EQU X.sub.i '=X.sub.i-1 +L.sub.0 .multidot.cos .theta..sub.i EQU Y.sub.i '=Y.sub.i-1 +L.sub.0 .multidot.sin .theta..sub.i
In this instance, first a link which is an element or segment which forms the road and which satisfies the following requirements is searched for. In particular, the link is included within a radius of 200 m from the estimated vehicle position P.sub.i '; a normal line can be drawn to the link; the link defines an angle within a fixed range (for example, within 45.degree.) with respect to the estimated vehicle orientation .theta..sub.i at the estimated vehicle position P.sub.i '; and the normal line drawn from the estimated vehicle position P.sub.i ' to the link is within a fixed distance (for example, 100 m). Here, a link Lka1 (straight line interconnecting nodes Na.sub.0 and Na.sub.1) of an orientation .theta.a.sub.1 on a road Rda and another link Lkb1 (straight line interconnecting nodes Nb.sub.0 and Nb.sub.1) of another orientation .theta.b.sub.1 on another road Rdb are searched out. Second, the lengths of normal lines Rlia and Rlib drawn from the estimated vehicle position P.sub.i ' to the links Lka.sub.1 and Lkb.sub.1, are calculated. Third, a coefficient Z is calculated using a suitable one of the following equations: EQU Z=dL.multidot.20+d.theta..multidot.20 (d.theta..ltoreq.35.degree.)(4) EQU Z=dL.multidot.20+d.theta..multidot.40 (d.theta.&gt;35.degree.)(4)'
where dL is the length of a normal line drawn from the estimated vehicle position P.sub.i ' to a link (distance from the estimated vehicle position to the link), and d.theta. is the angle defined by the estimated vehicle orientation .theta..sub.i and the link. As the angle d.theta. increases, the weighting coefficient increases.
Fourth, after the coefficient values Z are obtained, the links are determined which satisfy the following equations (1), (2) and (3):
(1) the distance dL.ltoreq.75 m (maximum drawing distance: 75 m)
(2) the angular difference d.theta..ltoreq.30.degree. (maximum drawing angle: 30.degree.) and
(3) the coefficient value Z.ltoreq.1,500.
Then, one of the links whose coefficient value exhibits the lowest value is determined as a matching candidate (optimum road). Here, the link Lka.sub.1 is determined as a matching candidate. Fifth, a traveling locus interconnecting the points P.sub.i-1, and P.sub.i ' is parallely moved in the direction of the normal line Rlia until the point P.sub.i-1 comes to a point on the link Lka1 (or on an extension line of the link Lka.sub.1) to determine movement points PT.sub.i-1 and PT.sub.i ' of the points P.sub.i-1 and P.sub.i '. Finally, the point PT.sub.i-1 is moved along an arc centered at the point PT.sub.i-1 until it comes to a point on the link LKa.sub.1 or the extension line of the link Lka1, to determine a moved point, which is determined as the actual vehicle position P.sub.i (X.sub.i, Y.sub.i). It is to be noted that the vehicle orientation at the actual vehicle position P.sub.i is determined to remain .theta..sub.i. On the other hand, when the P.sub.i-1 which is the vehicle position in the immediately preceding detection cycle remains on the road RDa, the moved point PT.sub.i-1 coincides with the point P.sub.i-1.
In a navigation apparatus, it is continually checked whether or not an optimum road determined by map matching processing forms a guide route, and if the optimum road does not form the guide route, then it is determined that the vehicle has gone out of the guide route and has entered an off-route condition. If an off-route condition is entered, and if the navigation apparatus is in an automatic route search mode, it immediately detects, based on the vehicle position, one of nodes on the guide route which has not been passed as yet and exhibits the smallest linear distance from the vehicle position, that is, a return point, and searched for a route along which the vehicle is to be guided from the vehicle position to the return point. The navigation apparatus then guides the vehicle to the guide route along the route thus searched out. On the other hand, if the navigation apparatus is not in an automatic route search mode, the driver will manually operate a remote controller or some other element to instruct the navigation apparatus to search for a route. In response to the instruction, the navigation apparatus detects a return point, searches for a route along which the vehicle is to be guided from the vehicle position to the return point, and guides the vehicle to the guide route along the route thus searched out.
However, conventional route searching when a vehicle is in an off-route condition, has various problems.
The first problem resides in that it sometimes occurs that the shortest route for the vehicle to return to the guide route cannot be selected. FIG. 22 illustrates an example of one of such situations. Referring to FIG. 22, if a vehicle travels on a guide route NVRT indicated by a solid line and enters an off-route condition at a point CP, then if the navigation system is in an automatic route search mode, route searching is started immediately, but if the navigation system is not in an automatic route search mode, route searching is not started until the system is instructed to perform route searching. In the route searching, the navigation apparatus detects, as a return point, a non-passed node C on the guide route which exhibits the shortest rectilinear distance from the vehicle position (point A). Then, the navigation apparatus performs a search for a route from the vehicle position A to the return point C as indicated by a broken line and then guides the vehicle along the route thus searched out. However, the travel distance to the destination is shorter if the vehicle returns to the guide route NVRT along a route RT from the point A to a point B than when the route detected by the navigation apparatus is taken. In other words, the conventional method sometimes fails to select the shortest route for the vehicle to return to the guide route. It is to be noted that the reason why the route of CP.fwdarw.A.fwdarw.B is not selected upon initial guide route searching is that a road having comparatively a great width is preferentially selected.
The second problem resides in that a route to a return point becomes commonplace. In the conventional route searching, route searching is performed from both the vehicle position and the return point while the vehicle is traveling, and when the routes from both of them intersect each other, the two routes are synthesized to determine a route (broken line) along which the vehicle should return from the vehicle position to the return point. However, with the method just described, since the vehicle is traveling, the route is determined after the vehicle runs a considerable distance. Consequently, a second off-route condition may be entered, and the route searched out cannot be used.
The third problem resides in that, if an off-route condition is entered near the destination, then a route which guides the vehicle away from the destination or another route which makes the vehicle take a round about way to the destination, is searched out. FIGS. 23 and 24 illustrate such a situation. Referring to FIGS. 23 and 24, a guide route is denoted at NVRT (indicated by cross hatching), a vehicle is denoted at CR, and a destination is denoted at DSP. Referring first to FIG. 23, if an off-route condition from the guide route is entered, then if the navigation apparatus is in an automatic route search mode, route searching is started immediately. In this instance, since the node on the guide route which is nearest from the point A is the point B, if a route from the vehicle position A in the advancing direction toward the point B is searched for, a route indicated by the broken line is searched out and guides the vehicle away from the destination. On the other hand, referring to FIG. 24, if the vehicle enters an off-route condition from the guide route NVRT and the navigation apparatus is not in an automatic route search mode, then the navigation apparatus is instructed to perform route searching using a remote controller after the vehicle moves to the point A. Since the nearest node on the guide route is the node B (the destination is not on any node), a round about way from the point A to the point B is searched out.